Common rail fuel systems typically employ multiple fuel injectors connected to a common rail that is provided with high pressure fuel. These fuel injectors can be selectively actuated to inject precise quantities of fuel at precise timings into combustion chambers of an associated engine. In order to produce these precise injection events, it can be important to know the pressure of the fuel within the common rail just prior to the injection events. For example, the fuel pressure within the common rail can drive displacement and/or delivery control of an associated fuel pump to provide fuel flow sufficient for the injection event. Fuel pressure information can also be used to calculate an injection timing and an injection duration that results in the desired injection event. This fuel pressure information may be provided by a pressure sensor associated with the common rail.
During operation of the common rail fuel system, it is possible for the pressure sensor to fail or malfunction. Without a backup strategy in place to drive pump output and determine injection timing and duration, the engine could be rendered inoperable. In order to ensure that the engine remains at least somewhat operable in the event of pressure sensor failure, a backup strategy may be implemented that provides some continued operational capability (e.g., engine operation allowing minimal propulsion, steering, braking, etc.). One such system is described in U.S. Pat. No. 6,024,064 (the '064 patent) issued to Kato et al. on Feb. 15, 2000. The '064 patent describes a fuel system having a pressure sensor for sensing the fuel pressure in a common rail. When the pressure sensor fails, an associated high pressure fuel supply pump and/or injectors may be controlled in several different ways without depending on signals from the pressure sensor to provide a “limp-home” function. The first way includes monitoring engine speed and load, and controlling the high pressure fuel supply pump according to a 2-dimensional (2-D) map. The 2-D map is factory preset into a control unit and shows a required fuel pressure for each set of an engine speed and load. Fuel injection timing and pulse width (duration) are calculated according to engine speed and load. The second way includes operating the high pressure fuel supply pump at a fixed output and controlling only fuel injection and pulse width according to engine speed and load. The third way includes operating the high pressure pump at maximum output and controlling injection and pulse width under assumed maximum pressure conditions.
Although the fuel system of the '064 patent may provide some continued engine operational capability, it may be inefficient and potentially damaging to the engine employing the fuel system. In particular, the components of the fuel system and associated engine wear over time, and settings that may have been appropriate when tested on a new engine under lab conditions may not be appropriate for an older engine under field conditions. Further, the fuel system of the '064 patent does not limit injector performance that could potentially damage the associated engine during conditions of pressure sensor failure.
The fuel system of the present disclosure solves one or more of the problems set forth above.